Recording materials that employ color development through the reaction between a color-forming compound and a color-developing agent allow recording in a short time using a relatively simple apparatus without performing complicated treatments such as development and fixation and are thus widely used in thermal recording paper for output recording in facsimiles, printers, etc., or pressure-sensitive copying paper or the like for forms for simultaneous multiple copying. These recording materials are required to immediately develop colors, maintain the whiteness of an uncolored part (hereinafter, referred to as a “background”), and offer the high colorfastness of colored images. Particularly, recording materials excellent in the heat resistance of the background are desired in terms of long-term storage stability. For this purpose, attempts have been made to develop color-forming compounds, color-developing agents, storage stabilizers, etc. Nevertheless, recording materials that have well-balanced, sufficiently satisfactory color-developing sensitivity, background and image stabilities, etc., have not been found yet.
The present inventors have already proposed a recording material excellent in the heat resistance of the background using a diphenylsulfone derivative as a color-developing agent (see patent document 1), a recording material excellent in the light resistance of the background using a cinnamamide compound as a color-developing agent (see patent document 2), and a recording material excellent in image stability using a compound having repeat units as a color-developing agent (see patent document 3). However, a recording material having well-balanced color-developing properties, plasticizer resistance and oil resistance of colored images, etc., remains to be obtained.